C5+ condensates (i.e., hydrocarbon mixtures predominantly comprising C5, C6, and heavier hydrocarbons) are often produced in natural gas processing plants and can be sold as commodity as such condensates can often be processed to transportation fuels. Unfortunately, C5+ condensates produced from upstream facilities often contain relatively high amounts of undesirable mercaptans and higher vapor pressure components, and must therefore be further processed to meet the environmental and transportation specifications, including Reid Vapor Pressure (RVP) values, ASTM distillation end point temperatures, and maximum mercaptan contaminant contents.
For example, current C5+ condensate product specifications require the condensate to have an RVP of 12 psia and a sulfur content of no more than 100 ppm by weight, which often requires removal of most of the C5 and lighter components. As C5+ condensates are typically produced from high-pressure sour gas fields, relatively large quantities of C4, C5, and lighter hydrocarbons, and various sulfur contaminants are often present. Presently known methods of removing these lighter components generally result in reduction in condensate production and loss in product revenue. To remedy loss of revenue, many of the currently known gas processing configurations and methods are forced to implement additional processing steps. For example, C5+ condensates can be blended with low RVP naphtha to produce a blended product with a lower RVP. Alternatively, or additionally, the C5+ condensate stream can be hydro-processed for conversion and ultimately removal of the sulfur contaminants, all of which adds complexity to the oil/gas separation facilities and increases operating and capital costs.
Alternatively, plant configurations could be developed to produce a C5+ condensate from high-pressure hydrocarbon mixtures that meets the C5+ product specification without sacrificing production. However, despite several known configurations for gas condensate separation, configurations that produce a condensate that meets C5+ product specification without negative impact on economics have not yet been described. For example, U.S. Pat. No. 4,702,819 to Sharma et al. teaches use of dual fractionation zones in which the first fractionation zone employs a side reboiler and a vapor sides-stream. While such configurations allow for at least somewhat desirable levels of gas/liquid separation, the production of a low RVP C5+ condensate is still very difficult. In another known configuration, as exemplified in U.S. Pat. No. 4,462,813 to May et al., a multi-stage compressor is connected to a wellhead, refrigeration unit, and separators. Similar to Sharma's configuration, May's configuration is relatively inefficient and energy intensive and not suitable to produce C5+ condensates with low RVP specifications, particularly when processing high-pressure hydrocarbon mixtures comprising significant quantities of C5 and lighter components.
In still further known examples, as described in RE 33,408 or U.S. Pat. No. 4,507,133 to Khan et al., the vapor stream from a deethanizer is cooled to liquefaction and contacted with a vapor phase from the hydrocarbon feed stream to separate methane, ethane, and propane vapors from the feed. Similarly, as described in U.S. Pat. No. 6,658,893 to Mealey, the feed gas is cooled to liquefy the heavier components and at least some of the C2 and lighter components. Subsequent condensation and absorption steps then allow high recovery of LPG components (i.e., C3 and C4+). Such processes are often limited to high yields of C3 and C4+ components, and are generally not suitable for heavier C5+ condensate components.
Thus, while numerous configurations and methods for gas condensate hydrocarbon separation are known in the art, all or almost all of them suffer from one or more disadvantages. Therefore, there is still a need for improved configurations and methods for gas condensate separation, and especially for gas condensate separation from high-pressure hydrocarbon mixtures that must meet the vapor pressure requirements of the C5+ product.